This invention relates to the preparation of novel cluster complexes and their use as highly active and selective catalysts. More specifically, the present invention relates to the synthesis of bimetallic clusters of Cr, Mo or W with Fe, Co or Ni and their use as catalysts for hydrogenation of carbon monoxide.
2. Description of the Prior Art
In general, previously known catalysts for hydrogenation of carbon monoxide are selective for C.sub.1 compounds only (such as CH.sub.4 or CH.sub.3 OH) and non-selective with respect to high carbon number compounds producing complex mixtures. Since many of the components of such mixtures have either low commercial value or undesirable properties, they must be separated from the more desirable products to achieve commercial significant products. However, the necessary separation steps are costly and inconvenient.
With the prospects of syngas derived fuels and feedstocks as alternate hydrocarbon sources, whether from reformed methane or coal gasification, it is anticipated that chemistry based on CO and H.sub.2 will eventually replace petroleum as a source of chemical feedstocks and fuels. However, major problems exist with respect to syngas conversion processes including sulfur poisoning of the catalyst and lack of selectivity. For example, both methanation catalysts based on Ni and common Fisher-Tropsch (F.-T.) catalysts are extremely sensitive to poisoning by sulfur in the syngas feed stream as are the ZnO/Cu methanol synthesis catalysts. Therefore, the development of selective, sulfur-tolerant catalysts for syngas conversion is needed.
In general, metal sulfides (see; Mitchell, Catalysis (London) 1977, 1, 204-233) are known as catalysts and, in particular, iron-molydbenum-sulfur compounds and the like based on "sulfided " metal molybdates on oxide supports (see, Furimsky, Catal. Rev.-Sci. Eng. 1980, 22, 371 and DuBois et al J. Am. Chem. Soc. 1979, 101, 5245; Ibid 1980, 102, 7456) are suggested as possible hydrodesulfurization catalysts and (see; Coucouvanis et al, Acc. Chem. Res. 1981, 14, 20 and Muller et al, Angew. Chem., Int. Ed. Engl. 1981, 20, 934) as the nitrogenase cofactor. It is also generally known and reported (see; Vahrenkamp, Angew. Chem., Int. Ed. Engl. 1975, 14, 322) that the presence of sulfur ligands tend to stabilize metal clusters.
However, the typical heterobimetallic sulfur containing catalysts of the prior art (e.g., CoMoS system) is prepared either by coprecipitation or by sequential or simultaneous absorption of the metals (e.g., Co(NO.sub.3).sub.2 and ammonium heptamolybdate) on Al.sub.2 O.sub.3, followed by calcining and sulfidation. Prepared in this manner, the catalysts contain varying proportions of inactive metal (e.g., Co) in the oxide support, as well as in the active CoMoS phase and at high loading inactive metal sulfides (e.g., Co.sub.9 S.sub.8). Hence, it has been impossible to establish even the stoichiometry of the active phase. Further, prior to the present invention, the lack of a practical method for the synthesis of Cp.sub.2 Mo.sub.2 (.mu.-S).sub.2 (.mu.-SH).sub.2 has prevented the investigation and synthesis of cluster compounds based on this intermediate composition.